Encapsulated dies with enhanced thermal performance

ABSTRACT

The present disclosure relates to enhancing the thermal performance of encapsulated flip chip dies. According to an exemplary process, a plurality of flip chip dies are attached on a top surface of a carrier, and a first mold compound is applied over the top surface of the carrier to encapsulate the plurality of flip chip dies. The first mold compound is thinned down to expose a substrate of each flip chip die and the substrate of each flip chip die is then substantially etched away to provide an etched flip chip die that has an exposed surface at the bottom of a cavity. Next, a second mold compound with high thermal conductivity is applied to substantially fill each cavity and the top surface of the second mold compound is planarized. Finally, the encapsulated etched flip chip dies can be marked, singulated, and tested as a module.

RELATED APPLICATIONS

This application claims the benefit of U.S. provisional patent application No. 62/138,177, filed Mar. 25, 2015, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a packaging process, and more particularly to a packaging process to enhance thermal performance of encapsulated flip chip dies.

BACKGROUND

With the current popularity of portable communication devices and developed semiconductor fabrication technology, high speed and high performance transistors are more densely integrated on semiconductor dies. Consequently, the amount of heat generated by the semiconductor dies will increase significantly due to the large number of transistors integrated on the semiconductor dies, the large amount of power passing through the transistors, and the high operation speed of the transistors. Accordingly, it is desirable to package the semiconductor dies in a configuration for better heat dissipation.

Flip chip assembly technology is widely utilized in semiconductor packaging due to its preferable solder interconnection between flip chip dies and laminate, which eliminates the space needed for wire bonding and die surface area of a package and essentially reduces the overall size of the package. In addition, the elimination of wire connections and implementation of a shorter electrical path from the flip chip die to the laminate reduces undesired inductance and capacitance.

In flip-chip assembly, mold compounds, formulated from epoxy resins containing silica particulates, are used to encapsulate and underfill flip chip dies to protect the dies against damage from the outside environment. Some of the mold compounds can be used as a barrier withstanding chemistries such as potassium hydroxide (KOH), sodium hydroxide (NaOH) and acetylcholine (ACH) without breakdown; while some of the mold compounds having good thermal conductive features can be used for heat dissipation of dies.

To accommodate the increased heat generation of high performance dies and to utilize the advantages of flip chip assembly, it is therefore an object of the present disclosure to provide a method to package flip chip dies in a configuration for better heat dissipation. In addition, there is also a need to enhance the thermal performance of encapsulated flip chip dies without increasing the package size.

SUMMARY

The present disclosure relates to enhancing the thermal performance of encapsulated flip chip dies. According to an exemplary process, a plurality of flip chip dies are attached on a top surface of a carrier, and a first mold compound is applied over the top surface of the carrier to encapsulate the plurality of flip chip dies. The first mold compound is thinned down to expose a substrate of each flip chip die and a wet/dry etchant material is used to etch away substantially the entire substrate of each flip chip die to provide an etched flip chip die that has an exposed surface at the bottom of a cavity. Next, a second mold compound is applied to substantially fill each cavity and directly contact the exposed surface of the etched flip chip die. The second mold compound is a high thermal conductivity mold compound, which improves thermal performance. The top surface of the second mold compound is then planarized. Finally, the encapsulated etched flip chip dies can be marked, singulated, and tested as a module.

Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

FIG. 1 provides a flow diagram that illustrates an exemplary etching and filling process according to one embodiment of the present disclosure.

FIGS. 2-8 illustrate the steps associated with the etching and filling process provided in FIG. 1.

FIG. 9 illustrates an exemplary application of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being “over” or extending “over” another element, it can be directly over or extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly over” or extending “directly over” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including” when used herein specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

The present disclosure relates to a method to enhance the thermal performance of encapsulated flip chip dies. FIG. 1 provides a flow diagram that illustrates an exemplary etching and filling process according to one embodiment of the present disclosure. FIGS. 2-8 illustrate the steps associated with the etching and filling process provided in FIG. 1. Although various types of materials may be used for the substrate, the following examples incorporate silicon as the preferred material. Initially, a plurality of flip chip dies 10 are attached on a top surface of a carrier 12 as depicted in FIG. 2 (Step 100). The carrier of the described embodiment is formed from a laminate, but may also be formed from a wafer level fan out (WLFO) carrier, a lead frame, a ceramic carrier, or the like. For the purpose of this illustration, each flip chip die 10 includes a substrate 14 with approximately 150-500 μm thickness, a device layer 16 with approximately 4-7 μm thickness, layer contacts 18 located on a bottom surface of the device layer 16, and solder interconnections 20 provided on each of the layer contacts 18. The device layer 16 may be formed from silicon dioxide, gallium arsenide, gallium nitride, silicon germanium, and the like and includes various devices, such as diodes, transistors, mechanical switches, resonators, and the like. The carrier 12 includes a carrier body 22, carrier contacts 24 on a top surface of the carrier 12 and input/output (I/O) pads (not shown) on a bottom surface of the carrier 12. The I/O pads on the bottom surface of the carrier 12 may be formed by a ball grid array (BGA) or land grid array (LGA) method and selectively connect to the carrier contacts 24 through any number of vias (not shown). The solder interconnections 20 of the flip chip dies 10 are used to electrically and physically connect to the carrier contacts 24 of the carrier 12. As such, the backside of the substrate 14 of the plurality of flip chip dies 10 will generally be the tallest component after the attaching process. The height between the device layer 16 and the carrier body 22 often varies from 15-200 μm.

A first mold compound 26 is then applied over the top surface of the carrier 12 such that the flip chip dies 10 are encapsulated by the first mold compound 26 as illustrated in FIG. 3 (Step 102). The first mold compound 26 may be applied by various procedures, such as sheet molding, overmolding, compression molding, transfer molding, dam fill encapsulation and screen print encapsulation. The first mold compound 26 is an organic epoxy resin system or the like, such as Hitachi Chemical Electronic Materials GE-100LFC, which can be used as an etchant barrier to protect the flip chip dies 10 against etching chemistries such as KOH, NaOH and ACH. A curing process (Step 104) is then used to harden the first mold compound.

With reference to FIGS. 4 through 6, a process for etching away substantially the entire substrate 14 of each encapsulated flip chip die 10 is provided according to one embodiment of the present disclosure. The process begins by forming a protective coating 28 over the bottom surface of the carrier 12, as shown in FIG. 4 (Step 106). The purpose of the protective coating 28 is to prevent potential damage to the I/O pads (not shown) on the bottom surface of the carrier 12 in subsequent processing steps. The protective coating 28 may be a chemical resistant tape or liquid protective coating, which can withstand etching chemistries such as KOH, NaOH and ACH without breakdown. Alternately, a rigid carrier can be sealed on the bottom surface of the carrier 12 as a protective coating 28 to prevent the I/O pads (not shown) on the bottom surface of the carrier 12 from contacting the destructive etchant materials in later etching processes.

The next process step is to thin the first mold compound 26 down to expose the back side of the flip chip dies 10, wherein the only exposed component of the flip chip dies 10 will be the substrate 14, as shown in FIG. 5 (Step 108). The thinning procedure may be done with a mechanical process. An alternate process step would be to leave the back side of the flip chip dies 10 always exposed during the molding process with the first mold compound 26.

Next, a wet/dry etchant chemistry, which may be KOH, ACH, NaOH or the like, is used to etch away substantially the entire substrate 14 of each flip chip die 10 to provide an etched flip chip die 10E that has an exposed surface at the bottom of a cavity, as shown in FIG. 6 (Step 110). Herein, etching away substantially the entire substrate 14 refers to removal of at least 95% of the entire substrate 14, and perhaps a portion of the device layer 16. As such, in some applications, there is a thin layer of the substrate 14 left at the bottom of the cavity of each etched flip chip die 10E, which covers the device layer 16, to protect the devices located on the device layer 16. For other cases, the substrate 14 is etched away completely and the device layer 16 is exposed at the bottom of the cavity of each etched flip chip die 10E.

With reference to FIGS. 7 through 9, a process for filling the remaining cavity of each etched flip chip die 10E is provided according to one embodiment of the present disclosure. After the etching step is done, a second mold compound 30 is applied to substantially fill the remaining cavity of each etched flip chip die 10E, as illustrated in FIG. 7 (Step 112). The second mold compound 30 may be applied by various procedures, such as sheet molding, overmolding, compression molding, transfer molding, dam fill encapsulation, and screen print encapsulation. The second mold compound 30 is a high thermal conductivity mold compound. Compared to the normal mold compound having 1 w/m·k thermal conductivity, a high thermal conductivity mold compound has 2.5 w/m·k-10 w/m·k or greater thermal conductivity, such as Hitachi Chemical Electronic Materials GE-506HT. The higher the thermal conductivity, the better the heat dissipation performance of the encapsulated etched flip chip dies 10E. Additionally, the second mold compound 30 directly contacts the exposed surface of each etched flip chip die 10E at the bottom of each cavity. If the substrate 14 is removed completely in the etching step (Step 110), the second mold compound 30 directly contacts the device layer 16. If there is a thin layer of substrate 14 left in the etching step (Step 110), the second mold compound 30 directly contacts the thin layer of substrate 14. Notably, the first mold compound 26 could be formed from the same material as the second mold compound 30. However, unlike the second mold compound 30, the first mold compound 26 does not have a thermal conductivity requirement in higher performing embodiments. A curing process (Step 114) is then provided to harden the second mold compound. The normal curing temperature is 175° F. and could be higher or lower depending on which material is used as the second mold compound 30.

The top surface of the second mold compound 30 is then planarized to ensure each encapsulated etched flip chip die 10E has a flat top surface as shown in FIG. 8 (Step 116). A package grinding process may be used for planarization. Next, the protective coating 28 applied over the bottom surface of the carrier 12 is removed as illustrated in FIG. 9 (Step 118). Lastly, the product could be marked, singulated and tested as a module (Step 120).

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow. 

What is claimed is:
 1. A method comprising: attaching a plurality of flip chip dies on a top surface of a carrier; applying a first mold compound over the top surface of the carrier to encapsulate the plurality of flip chip dies; thinning the first mold compound down to expose substrates of the plurality of flip chip dies; etching away substantially the entire substrate of each of the plurality of flip chip dies with an etchant to provide an etched flip chip die that has an exposed surface at the bottom of a cavity; and applying a second mold compound to substantially fill each cavity and directly contact the exposed surface of each etched flip chip die.
 2. The method of claim 1 wherein the carrier is one of a group consisting of a laminate, a wafer level fan out (WLFO) carrier, a lead frame, and a ceramic carrier.
 3. The method of claim 1 wherein the first mold compound is an organic epoxy resin system.
 4. The method of claim 1 wherein a thickness of the substrate of each of the plurality of flip chip dies is 150-500 μm.
 5. The method of claim 1 wherein the first mold compound is resistant to the etchant.
 6. The method of claim 1 wherein the exposed surface at the bottom of the cavity is a top surface of a device layer of each etched flip chip die.
 7. The method of claim 6 wherein the device layer includes at least one of a group consisting of diodes, transistors, mechanical switches, and resonators.
 8. The method of claim 6 wherein a thickness of the device layer is 4-7 μm.
 9. The method of claim 1 wherein the second mold compound has high thermal conductivity between 2.5 w/m·k and 10 w/m·k.
 10. The method of claim 1 wherein the first mold compound is formed from a first material, and the second mold compound is formed from the first material.
 11. The method of claim 1 wherein applying the first mold compound over the top surface of the carrier to encapsulate the plurality of flip chip dies is provided by sheet molding.
 12. The method of claim 1 wherein applying the first mold compound over the top surface of the carrier to encapsulate the plurality of flip chip dies is provided by overmolding.
 13. The method of claim 1 wherein applying the first mold compound over the top surface of the carrier to encapsulate the plurality of flip chip dies is provided by compression molding.
 14. The method of claim 1 wherein applying the second mold compound to substantially fill each cavity is provided by sheet molding.
 15. The method of claim 1 wherein applying the second mold compound to substantially fill each cavity is provided by overmolding.
 16. The method of claim 1 wherein applying the second mold compound to substantially fill each cavity is provided by compression molding.
 17. The method of claim 1 further comprising applying a protective coating over a bottom surface of the carrier.
 18. The method of claim 17 further comprising removing the protective coating over the bottom surface of the carrier.
 19. The method of claim 17 wherein the protective coating is one of a group consisting of a chemical resistant tape, a liquid protective coating, and a rigid protective carrier.
 20. The method of claim 1 further comprising planarizing a top surface of the second mold compound.
 21. The method of claim 1 wherein the first mold compound and the second mold compound are formed from different materials.
 22. The method of claim 21 wherein the second mold compound has a thermal conductivity between 2.5 w/m·k and 10 w/m·k.
 23. The method of claim 21 wherein the second mold compound has a thermal conductivity greater than 2.5 w/m·k.
 24. The method of claim 22 wherein the second mold compound has a thermal conductivity greater than 10 w/m·k.
 25. The method of claim 21 wherein the first mold compound is resistant to the etchant.
 26. The method of claim 1 wherein the second mold compound has a thermal conductivity greater than 2.5 w/m·k.
 27. The method of claim 1 wherein the second mold compound has a thermal conductivity greater than 10 w/m·k. 